1. Field of the Invention
The present invention relates to a multiple optical-axis photoelectric sensor for forming a light curtain that detects invasion into a hazardous region in order to prevent inadvertent access to a hazardous source such as a press machine.
2. Description of Related Art
A multiple optical-axis photoelectric sensor is often used for ensuring the safety of a machine regarded as a hazardous source such as a press machine. The multiple optical-axis photoelectric sensor is generally configured by a pair of a transmitter and a receiver, and these transmitter and receiver form a light curtain. The light curtain has a plurality of optical axes, and light interception of the optical axis is detected to thereby forcibly suspend the operation of the hazardous source.
In recent years, there are an increasing number of multiple optical-axis photoelectric sensors adopting infrared optical axes. In the multiple optical-axis photoelectric sensor using infrared rays, the presence of the light curtain is not visible, and hence there has been proposed a multiple optical-axis photoelectric sensor provided with a row of indicators on the same axis as a row of optical axes and arranged adjacent to the optical axes (Japanese Unexamined Patent Publication No. 2008-181788).
Further, there has already been proposed a multiple optical-axis photoelectric sensor including indicators that display various errors (Japanese Unexamined Patent Publication No. H11-345548). As for the indicators disclosed in Japanese Unexamined Patent Publication No. H11-345548, a plurality of narrow indicators are longitudinally arrayed in a bar form on the side surface of a case for the multiple optical-axis photoelectric sensor, and by means of lighting patterns of these indicators in the bar form, it is possible to perform a state display of a light-receiving amount shortage, reception of disturbance light, and other abnormalities, in addition to the presence or absence of light interception.
Japanese Unexamined Patent Publication No. 2009-10817 discloses a multiple optical-axis photoelectric sensor provided with a pair of hard projections on both sides of a detection surface located on a front surface of a case for the multiple optical-axis photoelectric sensor. In this multiple optical-axis photoelectric sensor provided with the pair of projections, even when a bar collides with the front surface, for example, the bar is received by the pair of projections, thereby allowing prevention of the detection surface from being damaged.
When a wide light curtain is to be made, in the example of a multiple optical-axis photoelectric sensor configured by a transmitter and a receiver as a typical example, a spacing between the transmitter and the receiver is set to be relatively large (lengthening of the range of the maximum allowable span). In the multiple optical-axis photoelectric sensor that allows the range-lengthening, it is necessary to increase a light amount of the light-projecting element, increase a size of a lens that is installed in front of the light-projecting element, and enhance the light-receiving sensitivity. Meanwhile, it is also necessary to enlarge a state display disposed in the multiple optical-axis photoelectric sensor, so as to enhance visibility.
However, in the case of designing the case for the multiple optical-axis photoelectric sensor to be as slim as possible, how and where in the case for the multiple optical-axis photoelectric sensor the indicators for performing a state display are arranged become a technical object.
A principal part of the elongated case for the multiple optical-axis photoelectric sensor is often made of an extrusion-molded article, and installing the indicator in this extrusion-molded article portion not only requires post-processing such as opening a hole in the extrusion-molded article, but may also cause weakening of the case.
Further, in each of recent multiple optical-axis photoelectric sensors, an inter-optical-axis pitch tends to be made shorter so as to ensure advanced safety, and associated with this, package densities of the light-projecting element and the light-receiving element housed inside the case are made higher. Naturally, there is also a demand for downsizing of the multiple optical-axis photoelectric sensor, thereby making it increasingly difficult to ensure a space for installation of the indicators.